JP2002078331A - Switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce low-frequency ripple voltage, without deteriorating the stability of a control system. SOLUTION: A low-frequency ripple voltage detection circuit 9, comprising a capacitor Cr and a resistor Rr connected in series to each other, is provided on the rear stage of a ripple voltage reducing circuit 8, which is a filter comprising an inductor L1 and a capacitor C1. A low-frequency ripple voltage, which cannot be completely reduced by the ripple voltage reducing circuit 8 is detected and the detected low-frequency ripple voltage is fed back to the control system for an output voltage, having switching devices 11 and 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply for reducing a low-frequency ripple voltage included in an output voltage.

[0002]

2. Description of the Related Art FIG. 4 is a diagram showing a configuration of a current resonance type switching power supply as an example of the prior art. The switching power supply of FIG. 1 includes a commercial power supply 1, an input filter 2, a rectifying and smoothing circuit 3, a control circuit 4, a DC-DC
Converter 5, phase correction circuit 7, and inductance L
1, divided resistors R1 and R2, an error amplifier circuit 6, and a load 10.

[0003] The AC voltage from the commercial power supply 1 is filtered by an input filter 2 and converted into a DC voltage by a rectifying / smoothing circuit 3. The DC-DC converter 5 converts the DC voltage into a high-frequency AC voltage, transforms the DC voltage, and returns the DC voltage to the DC voltage. The DC voltage output from the DC-DC converter 5 is
The phase is stabilized by the phase correction circuit 7 formed by the phase lead capacitor Cs and the resistor Rs, and the ripple voltage, which is an AC component included in the DC voltage, is reduced. The ripple voltage is also reduced by the inductance L1, and the output voltage Vo
Is supplied to the load 10 via the capacitor C1.

The output voltage Vo is divided by dividing resistors R1 and R2 and input to the error amplifier 6. Error amplifier 6
Then, the divided voltage is compared with the reference voltage to determine an error, amplify the error, and output it to the control circuit 4. The control circuit 4 controls the DC-DC based on the error signal from the error amplifier 6.
By controlling the on / off of the switching element installed inside the converter 5, the DC voltage value output from the DC-DC converter is adjusted. Thus, the negative feedback control is performed so that the output voltage Vo becomes a predetermined value.

In such a switching power supply, the ripple voltage included in the output voltage Vo depends on constants such as the phase lead capacitor Cs and the inductance L1. Ten meters
The value is about several hundred mV from V.

[0006] With respect to this ripple voltage, the phase lead capacitor Cs and the inductance L1 change from several tens of kHz to several hundreds of kHz.
It is possible to reduce a ripple voltage of a high frequency component of about Hz.

[0007]

However, the phase lead capacitor Cs and the inductance L1 have a problem that the output voltage of the commercial power supply 1 cannot reduce a low-frequency ripple voltage from 50 Hz to about 120 Hz. This is because the value of the inductance L1 which greatly contributes to the reduction of the ripple voltage is, for example, about 10 μH as a practically usable value, and is therefore too small to contribute to the reduction of the low-frequency ripple voltage. .

In order to reduce the low-frequency ripple voltage, it is conceivable to increase the gain of the error amplifier circuit 6. However, simply increasing the gain impairs the stability of the negative feedback control. As another method of reducing the low-frequency ripple voltage, a dropper power supply device such as a three-terminal regulator may be connected in series to the positive line connected to the load 10. However, since power loss occurs in the dropper power supply, power efficiency is reduced and the circuit scale is significantly increased.

The present invention has been made in view of the above, and an object of the present invention is to provide a switching power supply device capable of reducing a low-frequency ripple voltage without impairing the stability and power efficiency of a control system. It is in.

[0010]

A first feature of the present invention is as follows.
In a switching power supply device that converts an input voltage to an output voltage of a predetermined value by controlling on / off of a switching element, a reduction unit that reduces a ripple voltage included in the output voltage, and the reduction unit cannot completely reduce the ripple voltage. Detecting means for detecting the low-frequency ripple voltage, and means for feeding back the low-frequency ripple voltage detected by the detecting means to the control of the switching element.

According to a first feature of the present invention, a low-frequency ripple voltage that cannot be reduced by the reducing means is detected, and the low-frequency ripple voltage is fed back to control of a switching element. Since feedback control is performed on the output voltage based on the low-frequency ripple voltage detected for the output voltage supplied to the load, the low-frequency ripple voltage can be reduced without impairing the stability and power efficiency of the control system. .

A second feature of the present invention is a switching power supply device for converting an input voltage to an output voltage of a predetermined value and supplying the output voltage to a plurality of loads by controlling on / off of a switching element. Reducing means for reducing a ripple voltage included in each output voltage supplied to the detecting means, detecting means for detecting a low-frequency ripple voltage which cannot be reduced by the reducing means, and low-frequency ripple detected by the detecting means. Means for feeding back a voltage to the control of the switching element.

According to a second feature of the present invention, a low-frequency ripple voltage included in each output voltage supplied to a plurality of loads that cannot be reduced by the reducing means is detected, and the low-frequency ripple voltage is detected. Is fed back to the control of the switching element, so that even when there are a plurality of loads that supply the output voltage, the output voltage is output based on the low-frequency ripple voltage detected for each output voltage supplied to each load. Since feedback control is applied, the low-frequency ripple voltage can be reduced without impairing the stability and power efficiency of the control system.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] FIG. 1 is a diagram showing a configuration of a switching power supply according to a first embodiment. The characteristic of the switching power supply is that a low-frequency ripple is provided downstream of a ripple voltage reduction circuit 8. A voltage detecting circuit for detecting a low-frequency ripple voltage which cannot be reduced by the ripple voltage reducing circuit;
This low-frequency ripple voltage is supplied to the error amplifier 6 and the control circuit 4.
The control is fed back to the control of the output voltage by the DC-DC converter 5 via.

Hereinafter, the configuration and operation of each block will be described in detail. Note that the same components as those in FIG. 4 are denoted by the same reference numerals, and redundant description will be omitted.

The DC-DC converter 5 is a switching element 1 for converting a DC voltage into a square wave AC voltage.
1, 12, inductance 13, resonance capacitor 1
6. Capacitor 14, a transformer 15 for converting the amplitude of the AC voltage to an amplitude of a fixed magnification, rectifying diodes 17 and 18 for converting the AC voltage to a DC voltage, and a smoothing capacitor 19 for stabilizing the DC voltage. Configuration.
In the figure, MOSFETs are used as the switching elements 11 and 12 as an example, but the present invention is not limited to this, and various semiconductor switching elements may be used.

The drain terminal of the switching element 11 is connected to the positive terminal of the rectifying / smoothing circuit 3, and the source terminal is connected to the drain terminal of the switching element 12. The source terminal of the switching element 12 is connected to the negative terminal of the rectifying / smoothing circuit 3.

One terminal of a primary side transformer 15a of the transformer 15 is connected to a connection point between the switching elements 11 and 12 via an inductance 13, and is connected to the primary side transformer 15a.
The other terminal a is connected to the negative terminal of the rectifying / smoothing circuit 3 via the resonance capacitor 16.

The secondary side of the transformer 15 is formed by secondary side transformers 15b and 15c connected in series. The cathode terminal of the rectifier diode 17 whose anode terminal is connected to the other terminal of the secondary transformer 15b and the cathode terminal of the rectifier diode 18 whose anode terminal is connected to the other terminal of the secondary transformer 15c have positive poles, respectively. And connected to one terminal of the load 10 via the inductance L1 on the positive line.
The other terminal of the load 10 is connected to a connection point between the transformers 15b and 15c via a negative polarity line.

The on time and off time of the switching elements 11 and 12 are controlled by a control signal from the control circuit 4. When the switching element 11 is turned on, the switching element 12 is turned off, energy is stored in the inductance 13 and the capacitor 16 and a current flows through the primary transformer 15a. On the other hand, the switching element 11
Is turned off, the switching element 12 is turned on, and the energy stored in the inductance 13 and the capacitor 16 is released, so that the primary transformer 15a
Current in the opposite direction. As a result, a square wave AC voltage is generated. This AC voltage is converted into an amplitude of a fixed magnification by the transformer 15, and is converted into a DC voltage by the rectifier diodes 17 and 18.

As described above, in the DC-DC converter 5, the output voltage value is adjusted by changing the time width of the square wave based on the control signal from the control circuit 4.

The error amplifier 6 has an operational amplifier 20, a reference voltage Ref, a resistor 22, and a capacitor 21. The resistor 22 and the capacitor 21 are connected to the operational amplifier 2
The inverting input terminal of the operational amplifier 20 is connected in series with a connection point between the dividing resistors R1 and R2 for dividing the output voltage Vo. The reference voltage Ref is connected to the non-inverting input terminal, and the output terminal of the operational amplifier 20 is connected to the control circuit 4.

The phase correction circuit 7 is formed by a phase lead capacitor Cs and a resistor Rs connected in series, and the other terminal of the capacitor Cs is connected to a positive line and a resistor Rs
The other terminal of s is connected to the inverting input terminal of the operational amplifier 20. The phase lead capacitor Cs reduces the high frequency ripple voltage.

The ripple voltage reduction circuit 8 is a filter formed by an inductance L1 connected in series with the positive polarity line and a smoothing capacitor C1 connected in parallel with the load 10, and is more effective than the phase lead capacitor Cs in the high frequency ripple. Reduce voltage.

The low-frequency ripple voltage detecting circuit 9 is formed by a capacitor Cr and a resistor Rr connected in series, and the other terminal of the capacitor Cr is connected to a positive line,
The other terminal of r is connected to the inverting input terminal of the operational amplifier 20.

The capacitor Cr detects a low-frequency ripple voltage that cannot be reduced by the ripple reduction circuit 8, and converts the low-frequency ripple voltage to an output voltage Vo divided by the division resistors R1 and R2 via the resistor Rr. Superimposed operational amplifier 20
Output to the inverted input terminal.

The operational amplifier 20 compares the voltage input to the inverting input terminal with the reference voltage Ref, amplifies the error and outputs the result to the control circuit 4. The control circuit 4 controls ON / OFF of the switching elements 11 and 12 based on the error signal so that the output voltage Vo becomes a predetermined value.

Therefore, according to the present embodiment, the low-frequency ripple voltage that has not been reduced by the ripple voltage reduction circuit 8 is detected by the low-frequency ripple voltage detection circuit 9, and this low-frequency ripple voltage is detected by the switching element 11. 12, the feedback control is performed on the output voltage Vo based on the low-frequency ripple voltage detected for the output voltage supplied to the load 10, so that the stability and power efficiency of the control system are improved. , The low-frequency ripple voltage can be reduced.

In the present embodiment, the ripple voltage reduction circuit 8 is a single-stage filter, but may be a multi-stage configuration in which a plurality of filters are connected as shown in FIG. In such a case, the low-frequency ripple voltage can be quickly reduced by adjusting each constant. However, the number of stages needs to be in a range where the feedback control system does not become unstable due to phase rotation.

[Second Embodiment] FIG. 3 is a diagram showing a configuration of a switching power supply unit to which the present invention is applied when there are a plurality of loads. In the figure, the same components as those in FIG. 1 are denoted by the same reference numerals, and the configuration and operation of blocks different from those in FIG. 1 will be described below.

The configuration of the DC-DC converter 31 is shown in FIG.
Is basically the same as the configuration of the DC-DC converter 5 shown in FIG. 2, but the configuration of the rectifier diode in the output stage is different in order to supply a DC voltage to the plurality of loads 33 and 34.

The secondary transformers 15b and 1b of the transformer 15
The ground line connected to the connection point with 5c is connected to the load 3
It is connected to the junction between 3 and 34. Secondary transformer 15b
The positive line connected to the positive terminal of the load 33 is connected to the positive terminal of the load 33 via the rectifier diode 35 and the inductance L3. The anode terminal of the rectifier diode 35 is connected to the positive terminal of the secondary transformer 15b. The negative line connected to the negative terminal of the secondary transformer 15c is connected to the negative terminal of the load 34 via the rectifier diode 38 and the inductance L4. In the rectifier diode 38, the cathode terminal is connected to the negative terminal of the secondary transformer 15c.
The rectifier diode 36 has a cathode terminal connected to the positive line and an anode terminal connected to the negative terminal of the secondary transformer 15c. The rectifier diode 37 has an anode terminal connected to the negative line and a cathode terminal connected to the negative line.
Connected to the positive terminal of the next transformer 15b.

With this configuration, the load 33 is supplied with the positive voltage Vo, and the load 34 is supplied with the negative voltage -Vo.

The divided resistors R 1 and R 2 connected in series are connected in parallel to the loads 33 and 34, and output a voltage obtained by dividing the output voltage to the inverting input terminal of the operational amplifier 20.

The inductance L3 connected in series to the positive line reduces the high-frequency ripple voltage included in the positive voltage Vo. Further, the inductance L4 connected in series to the negative line reduces the high-frequency ripple voltage included in the negative voltage -Vo.

The low-frequency ripple voltage detection circuit 32 is provided at a stage subsequent to the inductances L3 and L4. The capacitors Cr + and Cr- connected in series are connected in parallel to the loads 33 and 34, and the capacitors Cr + and Cr- are connected. In this configuration, the other end of the resistor Rr connected to the connection point is connected to the inverting input terminal of the operational amplifier 20. The capacitor Cr + detects a low frequency ripple voltage included in the positive voltage Vo, and the capacitor Cr− detects a low frequency ripple voltage included in the negative voltage −Vo. Here, the capacitors Cr + and Cr- have different capacities so that the low-frequency ripple voltages detected by the capacitors Cr + and Cr- do not cancel each other.

The low-frequency ripple voltage thus detected is input to the inverting input terminal of the operational amplifier 20 via the resistor Rr. Then, as described in the first embodiment, the low-frequency ripple voltage is fed back to the control of the output voltage by the switching elements 11 and 12 of the DC-DC converter 31 via the error amplifier 6 and the control circuit 4. Is reduced.

Therefore, according to the present embodiment, when there are a plurality of loads 33, 34, the inductance L3,
The output voltages Vo and -Vo that could not be reduced by L4
Is detected by the low-frequency ripple voltage detection circuit 32, and the low-frequency ripple voltage is fed back to the control of the switching elements 11 and 12, so that the low-frequency ripple voltage is supplied to the loads 33 and 34. Since the output voltage is subjected to feedback control based on the detected low-frequency ripple voltage for each output voltage, the low-frequency ripple voltage can be reduced without impairing the stability and power efficiency of the control system.

In this embodiment, the capacitors Cr + and Cr- have different capacities, but these capacities can be made equal by adjusting the values of the inductances L3 and L4.

In this embodiment, the high-frequency ripple voltage is reduced by the inductances L3 and L4, but a plurality of π-type filters as shown in FIG. 2 are connected in parallel to the loads 33 and 34, respectively. The configuration may be as follows. In such a case, the low-frequency ripple voltage can be quickly reduced by adjusting each constant.

[Application to Other Embodiments] In each of the above embodiments, the case where the present invention is applied to the current resonance type switching power supply device has been described. However, the present invention is not limited to this. , RCC type switching power supply device, FCC type switching power supply device and the like.

[0043]

As described above, according to the first aspect of the present invention, the feedback control is performed on the output voltage supplied to the load based on the detected low-frequency ripple voltage. And the low-frequency ripple voltage can be reduced without impairing the power efficiency.

According to the second feature of the present invention, even when there are a plurality of loads, the detected low-frequency ripple voltage is fed back with respect to the output voltage supplied to each load. The low-frequency ripple voltage can be reduced without impairing the efficiency.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a switching power supply device according to a first embodiment.

FIG. 2 is a diagram illustrating another configuration example of the ripple voltage reduction circuit.

FIG. 3 is a diagram illustrating a configuration of a switching power supply according to a second embodiment.

FIG. 4 is a diagram illustrating a configuration of a conventional switching power supply device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Commercial power supply 2 Input filter 3 Rectifier smoothing circuit 4 Control circuit 5, 31 DC-DC converter 6 Error amplifier 7 Phase correction circuit 8 Ripple voltage reduction circuit 9 Low frequency ripple voltage detection circuit 10, 33, 34 Load 11, 12 Switching element DESCRIPTION OF SYMBOLS 13 Inductance 14, 21, 39, 40 Capacitor 15 Transformer 16 Resonant capacitor 17, 18, 35, 36, 37, 38 Secondary rectifier diode 19, 39, 40 Smoothing capacitor 20 Operational amplifier 22 Resistance 32 Low frequency ripple voltage detection circuit Cs Phase lead capacitor Ref Reference voltage Cr capacitor Rs, Rr Resistance R1, R2 Dividing resistance L1, L2, L3, L4, Ln Inductance C1, C2, C3, C4, Cn Smoothing capacitor

Claims (2)

[Claims] 1. A switching power supply device for converting an input voltage to an output voltage of a predetermined value by controlling on / off of a switching element, a reducing unit for reducing a ripple voltage included in the output voltage, and the reducing unit. Switching means for detecting a low-frequency ripple voltage that has not been completely reduced by the following, and means for feeding back the low-frequency ripple voltage detected by the detecting means to control of the switching element. Power supply. 2. A switching power supply device for converting an input voltage into an output voltage having a predetermined value and supplying the output voltage to a plurality of loads by controlling ON / OFF of a switching element, wherein each output supplied to the plurality of loads is provided. A reducing unit configured to reduce a ripple voltage included in the voltage, a detecting unit configured to detect a low-frequency ripple voltage that cannot be reduced by the reducing unit, and controlling the switching element to control the low-frequency ripple voltage detected by the detecting unit. And a means for feeding back to the switching power supply.